Here is the honest part. If your door is a single steel panel from the early end of that 1958 to 2004 range and the bottom panel has rusted through, we are not going to sell you a new spring for it. Once the panel itself is failing, the door's weight distribution changes, and a fresh spring on a compromised section is money spent on a problem that comes right back within a few months.
Openers follow the same rule. If the circuit board is dead and the unit is old enough that the manufacturer no longer stocks parts for it, a replacement is usually cheaper than a repair that only buys you another year. A chain-drive unit from the 80s or 90s that has stripped a gear twice is past the point where another repair makes sense.
We will tell you straight when a job is not worth doing, even when that means a smaller invoice for us. Most calls across this area are a single-part fix - a spring near the end of its 10,000-cycle life, a stiff nylon roller, a cable frayed at the bottom bracket - not a full teardown. When replacement genuinely is the better value, we say so before any work begins rather than patching a door that will fail again next winter.